This invention relates to a flat sliding door unit used for furniture or fittings, and more particularly to a flat sliding door unit in which a sliding door is on the same vertical flat plane as that of the adjacent sliding door, or adjacent stationary wall when closed and, when intended to be opened, is shifted to the front side of the abovesaid adjacent sliding door or stationary wall.
A flat sliding door unit of the type wherein a door on one side, when intended to be opened, is swung like a hinged door to one side at one end thereof adjacent to the neighboring door and then slid sideways, is disclosed, for example, in Japanese Patent, Laid-open No. 141679/1984. In this unit, side lead-in rails are connected to the main rail extending in the right and the left directions at approximate right angles with respect to the main rail, and rollers fixed to abutting end portions of the sliding doors are mounted on slides fitted into these lead-in rails.
However, in this structure, noise is emitted from the junction of the slide and the main rail when the roller is shifted from the slide to the main rail, and a groove must be formed on the main rail for fitting the slide thereinto smoothly because the slide and the upper surface of the main rail must be flush with each other. Accordingly, unless a junction of the lead-in rail including the slide and the main rail are in considerably high precision, not only is rolling of the roller uneven and setting of the furniture is troublesome, but also a groove formed across the elongate main rail causes significant decrease in the rail strength. Moreover, this known structure encounters such problems that, since a roller supporting stay on the door on one side cannot pass through that on the door on the other side, installation of a roller stay at the leading end (the end of a door abutting on that of the other door) is impossible and a sliding door is hung at one side thereof, whereby the structure is unsuitable for the use in a heavy door. These problems are not limited to the sliding door unit of the two-step action type, i.e., swing-and-slide type, as described above but are also caused in known flat sliding door units of the type in which side rails are connected to the main rail.